Targeting the less competitive KWs is quite effective. those getting around 20-30k searches per month are good. But to profit substiantially you shud target quite a few more niches simultaneously.
One Example: If you read collinlahay.com then you will find he has started a BANS site on Super Nintendo Console.
Now this term is searched 22k times per month. He has not done anything to the website. It is not SEOed yet. But still it ranks 3rd i search results. He made already $7 in a week.
Now if you target 10 such keywords then you will be able to generate 70 bucks per week.
Moral of the story: Target the less popular and long tail keyword and SEO up your site.
Just my 2 cents.